1. Field of the Invention
The invention relates to a cryosurgical device and method for cooling surfaces by dispensing a liquid refrigerant through a shaped applicator of porous material, and more particularly, to a device having a dispensing system with a protective sheath such that refrigerant can only be discharged when the device is correctly assembled.
2. Description of the Related Art
It is known to provide localized freezing of a part of a human or animal body in order to remove a skin lesion such as a wart. Physicians have used liquid nitrogen applications to remove lesions from the skin. This method of treatment has been effective but suffers from the disadvantage of requiring specialized equipment to condense nitrogen, the need for specialized storage devices, and the inherent hazards of handling and dispensing a material having a boiling point of approximately −196° C. A certain amount of skill is required during treatment, so that excessive tissue injury does not occur.
More recently, methods were developed to treat skin lesions cryogenically by employing a liquid refrigerant contained in a pressurized container. In such methods, an effective amount of the cryogenic agent from the pressurized container is supplied into a hollow supply tube, having a cotton, fiber or plastic foam applicator located at the distal end of the tube, so that the cryogenic material accumulates in the applicator. The skin surface of the lesion is then contacted with the applicator having the accumulated cryogenic agent for a period of time sufficient to permit the cryogenic agent to reduce the temperature of the skin lesion tissue to temperatures that freeze the skin, such that permanent, irreversible rupture of cellular membranes of cells of the skin lesion occurs while the cryogenic agent is evaporating. Subsequently, the applicator is removed from the skin surface after a period of time that is generally about 20 to about 60 seconds, depending on the boiling point of the refrigerant and the depth of tissue that will be frozen, and the frozen skin tissue of the skin lesion is then permitted to slowly thaw. During the next several weeks, the tissue that was frozen dislodges from the surrounding skin.
Examples of devices for applying a cryogenic agent to a skin lesion are disclosed in U.S. Pat. No. 4,865,028 (Swart); U.S. Pat. No. 5,516,505 (McDow); U.S. Pat. No. 5,200,170 (McDow); U.S. Pat. No. 5,330,745 (McDow); U.S. Pat. No. 5,738,682 (Jensma); U.S. Pat. No. 6,296,410 (Ruizendaal); U.S. Pat. No. 6,092,527 (Jensma); U.S. Pat. No. 6,296,410 (Ruizendaal); U.S. Pat. No. 6,387,090 (Jensma); and U.S. Published Patent Application No. 2005/0043723 (Howlett et al.). The disclosures of these patents and application are herein incorporated by reference. U.S. Pat. No. 4,865,028 discloses a method and apparatus for delivering a therapeutic effect by delivering refrigerant through an applicator comprising a cotton wool bud surrounding the discharge end of the outlet of a tube and which is placed directly on or near the site to be treated. U.S. Pat. Nos. 6,092,527, 6,387,090 and 5,738,682 disclose a method and apparatus for providing a localized freezing of a wart or other growth. The Jensma patents disclose a shaped applicator tip composed of open celled foam and particularly an applicator comprised of open celled foam over cotton which is preferred for use in the present invention.
An operational feature of cryosurgical devices is the manner in which the cryogenic agent is moved from the container to the applicator. There should be little loss in the cryogenic material during transfer and, therefore, the cryogenic material should travel the most effective and shortest path in order to provide the greatest effectiveness in treating the skin lesion.